Detection of molecular transitions with nitrogen-vacancy centers and electron-spin labels
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-11-30 |
| Journal | npj Quantum Information |
| Authors | Carlos Munuera-Javaloy, Ricardo Puebla, Benjamin DâAnjou, Martin B. Plenio, J. Casanova |
| Institutions | Instituto de FĂsica Fundamental, UniversitĂ€t Ulm |
| Citations | 9 |
| Analysis | Full AI Review Included |
Technical Documentation: Nanoscale ESR Detection using Shallow NV Centers
Section titled âTechnical Documentation: Nanoscale ESR Detection using Shallow NV Centersâ6CCVD Material Analysis & Sales Strategy
This document analyzes the research detailing the detection of molecular transitions using shallow Nitrogen-Vacancy (NV) centers in diamond, focusing on the material requirements and how 6CCVDâs specialized MPCVD diamond products (SCD/PCD) can support and advance this cutting-edge quantum sensing application.
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates a robust protocol for nanoscale Electron Spin Resonance (ESR) detection of molecular dynamics using shallow NV centers in diamond.
- Core Value Proposition: Detection of single-molecule conformational transitions and dynamics at ambient (room) temperature using a modified Double Electron-Electron Resonance (DEER) sequence.
- Material Requirement: Requires high-quality Single Crystal Diamond (SCD) substrates featuring ultra-shallow, high-coherence NV centers (4 nm depth cited).
- Enhanced Robustness: Spectral interpretation is simplified and robustness against molecular tumbling is maximized by employing nitroxide labels containing distinct nitrogen isotopes (14N and 15N).
- Distance Measurement: The protocol successfully extracts inter-label distances ($d_{12}$) in the 3-4 nm range (e.g., 3.297 nm actual, 3.54(25) nm inferred) using Bayesian inference.
- Methodological Innovation: Residual molecular tumbling, typically detrimental, is leveraged as a resource to independently extract inter-label distance and orientation parameters.
- 6CCVD Solution: 6CCVD provides the necessary Optical Grade SCD substrates with industry-leading surface quality (Ra < 1nm) essential for maximizing the coherence of shallow NV sensors.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental simulations and material requirements detailed in the paper:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Depth | 4 | nm | Required for single-spin sensitivity near the diamond surface. |
| Applied Magnetic Field ($B^z$) | 30 | mT | Ensures stability of the robust E0 energy-transition branch. |
| NV Coherence Time ($T_{2}$) | 20 | ”s | Decoherence limit used in realistic ambient simulations. |
| Electron-Spin Label Relaxation ($T_{1}$) | 4 | ”s | Relaxation time used for nitroxide labels. |
| Free Evolution Time ($T_{free}$) | 1.3 | ”s | Duration of each free evolution stage in the DEER sequence. |
| Total Sequence Time | 4.6 | ”s | Total duration of the modified DEER pulse sequence. |
| RF Rabi Frequency ($\Omega_{RF}$) | 2Ï Ă 250 | kHz | Used for driving electronic resonances of the nitroxide labels. |
| Actual Inter-Label Distance ($d_{12}$) | 3.297 | nm | Distance used in the simulation model. |
| Inferred Inter-Label Distance ($d_{12}$) | 3.54(25) | nm | Result obtained via Bayesian inference. |
Key Methodologies
Section titled âKey MethodologiesâThe experimental approach relies on precise material engineering and a carefully optimized quantum sensing protocol:
- Material Preparation: High-pquality diamond substrate is required for controlled, ultra-shallow implantation of Nitrogen-Vacancy (NV) centers (target depth 4 nm).
- Magnetic Field Application: A moderate magnetic field ($B^z = 30$ mT) is applied along the z-axis to energetically suppress anisotropic hyperfine interaction effects while maintaining the stability of the robust E0 energy-transition branch.
- Spectroscopy Protocol: A modified Double Electron-Electron Resonance (DEER) sequence is employed, simultaneously delivering Microwave (MW) pulses to the NV center and Radiofrequency (RF) pulses to the nitroxide labels.
- Pulse Sequence Design: The sequence uses two free evolution stages ($T_{free}$) separated by a driving stage featuring 2N+1 MW $\pi$-pulses on the NV and a single RF $\pi$-pulse on the labels. This ensures constructive phase accumulation and averages out spurious NV-label interactions during irradiation.
- Orthogonal Labeling: The use of distinct nitrogen isotopes (14N and 15N) in the two nitroxide labels simplifies the inter-label interaction Hamiltonian, making the spectrum interpretation much simpler and more robust against molecular motion.
- Data Analysis: Bayesian inference (Markov Chain Monte Carlo sampling) is applied to the tumbling-averaged NV spectrum data to efficiently and independently extract the inter-label distance ($d_{12}$) and orientation angle ($\beta$).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the critical need for high-quality, engineered diamond substrates to enable robust nanoscale quantum sensing. 6CCVD is uniquely positioned to supply the materials required to replicate, scale, and advance this work.
Applicable Materials for Nanoscale ESR
Section titled âApplicable Materials for Nanoscale ESRâTo achieve the 4 nm NV depth and maintain the 20 ”s coherence time cited in the paper, the highest quality Single Crystal Diamond (SCD) is mandatory.
| 6CCVD Material Recommendation | Specification & Relevance |
|---|---|
| Optical Grade SCD | Ultra-high purity, low strain material essential for maximizing NV coherence ($T_{2}$). |
| Custom Polishing (Ra < 1nm) | Critical for shallow NV applications. Minimizing surface roughness (Ra < 1nm) reduces surface noise and decoherence mechanisms affecting the 4 nm deep NV centers. |
| Custom Thickness SCD | Available from 0.1 ”m up to 500 ”m, allowing researchers to optimize the diamond thickness based on implantation energy and thermal management requirements. |
| Custom Dimensions | SCD plates available in various sizes (e.g., 5x5 mm, 10x10 mm) suitable for integration into complex quantum sensing setups. |
Customization Potential for Advanced Research
Section titled âCustomization Potential for Advanced ResearchâThe complexity of the DEER protocol and the need for on-chip control structures require specialized material processing, which 6CCVD provides in-house.
- Custom Metalization Services: If the experimental setup requires integrated microwave or radiofrequency delivery structures (e.g., coplanar waveguides) near the NV center, 6CCVD offers internal metalization capabilities including Ti, Pt, Au, Pd, W, and Cu deposition.
- Precision Fabrication: 6CCVD provides custom laser cutting and shaping services, ensuring that the diamond substrate dimensions precisely match the requirements of the cryostat or magnetic field setup. We offer plates/wafers up to 125mm (PCD) and substrates up to 10mm thick.
- Boron Doping (BDD): For future extensions of this work involving electrochemical sensing or integrated conductive elements, 6CCVD offers custom Boron-Doped Diamond (BDD) films.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of MPCVD diamond for quantum applications. We can assist researchers in material selection for similar Nanoscale Magnetic Resonance Spectroscopy projects, ensuring optimal substrate quality, orientation, and surface preparation for subsequent shallow NV implantation and high-coherence operation.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract We present a protocol that detects molecular conformational changes with two nitroxide electron-spin labels and a nitrogen-vacancy (NV) center in diamond. More specifically, we demonstrate that the NV can detect energy shifts induced by the coupling between electron-spin labels. The protocol relies on the judicious application of microwave and radiofrequency pulses in a range of parameters that ensures stable nitroxide resonances. Furthermore, we demonstrate that our scheme is optimized by using nitroxides with distinct nitrogen isotopes. We develop a simple theoretical model that we combine with Bayesian inference techniques to demonstrate that our method enables the detection of conformational changes in ambient conditions including strong NV dephasing rates as a consequence of the diamond surface proximity and nitroxide thermalization mechanisms. Finally, we counter-intuitively show that with our method the small residual effect of random molecular tumbling becomes a resource that can be exploited to extract inter-label distances.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 1998 - Structure Elucidation by Modern NMR [Crossref]
- 1961 - The Principles of Nuclear Magnetism
- 2001 - Principles of pulsed electron paramagnetic resonance [Crossref]